Automatically tiltable small roller structure of slide bearing type

ABSTRACT

An automatically tiltable small roller structure, which comprises a shaft, a small roller including an elastic rubber cylinder and a sleeve, and a plurality of bearing balls. The sleeve is integral with the inner periphery of the elastic rubber cylinder, and mainly composed of polytetrafluoroethylene (fluoroplastics). The shaft is fitted in the roller structure. The bearing balls are fitted in a circumferential or annular groove formed on the shaft, and are provided such that they are in rolling contact with the inner periphery of the roller and the outer periphery of the shaft in the groove. The groove is provided at a middle point between the opposite ends of the roller. The depth of the groove is set such that the bearing balls project slightly from the groove, so that a slight gap is formed between the inner periphery of the roller and the outer periphery of the shaft. The axes of the roller and shaft are thus slightly tiltable in relation to each other.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to guide rollers and pinch rollers for guidingtapes of tape recorders and video tape recorders, and also other smallrollers used for guiding soft tapes and printer tapes of computers, wordprocessors, etc.

2. Prior Art

FIG. 10 shows a small roller A, which may be used as a guide roller or apinch roller for guiding magnetic tapes of a tape recorder or a videotape recorder. The small roller A consists of a light metal cylinder 1and an elastic rubber layer 2 provided thereon. The light metal cylinder1, which may be made of aluminum, is fitted on a shaft 3 via asuper-small ball bearing 4 or a radial bearing. Oil seals 5 are providedon the opposite sides of ball bearing 4. The small roller A isautomatically tiltable in a small range of about 1° or below withrespect to the shaft 3.

Although a super-small ball bearing 4 of high precision has recentlybeen manufactured by mass production, it does not meet user's requiementas to production costs. Further, because it is a type of radial bearing,it does not meet optimum requirements by users especially in having aautomatically tiltable property. The reason why the radial bearings areutilized in this field is only that they happen to provide an automatictilting action, although the action is done at a relatively narrowerrange.

Further, since the radial ball bearings require inner and outer rings 6and 7, it is impossible to reduce the outer diameter of such rollers,and therefore, it is impossible to substantially reduce the size ofapparatus utilizing these ball bearings.

Recently, rollers using tetrafluoride resins as bearing material havebeen announced. However, such rollers are incapable of automatic tiltingbecause they are of slide bearing support type, and hence they can notbe used as small rollers of the said type requiring automatic tiltingproperty.

Further, in the aspect of a PV value and coefficient of friction,materials having high mechanical strength are liable to cause wear ofthe opposing member, and they also cause heat generation. (The PV valueis obtained by multiplying P and V, where P=unit pressure of the shafton the bearing that is obtained by dividing the load on the bearing bythe projected bearing area. V=velocity of wear surface). Materialshaving low coefficient of friction, on the other hand, have insufficientmechanical strength. Therefore, both of such materials can be hardlyused as small rollers of the type noted above.

Particularly, rollers used for guiding video tape recorder tapes have tomeet strong demands for high speed rotation, capability of being usedfor long time, light weight (use of aluminum shaft), freedom fromlubrication, prevention of heat generation, low noise and low cost.Development of a small roller which can meet the above demands has beenexpected in the pertinent field.

SUMMARY OF THE INVENTION

An object of the invention is to provide a small roller of simpleconstruction, which uses fluoroplastics as a main material of the innerperiphery of roller, makes use of character of a slide bearing and hasan automatic tilting effect.

The small roller of the invention comprises an elastic rubber cylinderand a sleeve which is provided integrally on the inner side of therubber cylinder and composed of polytetrafluoroethylene (fluoroplastics)as a main component. The small roller is fitted on a shaft, and theshaft or the roller has a circumferential or annular groove. A pluralityof bearing balls are provided in this groove such that they can rol overan inner periphery of the small roller and an outer periphery of theshaft. The groove is provided at a position mid way between the oppositeends of the small roller. The groove has a depth such that the bearingballs slightly project from the groove, and a slight gap is formedbetween the roller inner periphery and the shaft outer periphery. Theaxes of the two members are slightly tiltable relative to each other, soas to obtain an automatically tiltable small roller structure of slidebearing type, and thereby the problems inherent in the prior art aresolved.

With the above construction according to the invention, the roller andthe shaft can tilt or rock slightly relative to each other for a rangeof gap dimension between them about the row of bearing balls, and theroller can rotate about the shaft while they are undergoinginstantaneous changes in their relative orientation.

With the above construction and effect, corresponding to forces receivedexternally by them, the roller and the shaft may be supported only bythe row of bearing balls contacting a mid portion of the inner peripheryof the sleeve, or supported by both the bearing ball row and a portionof the inner periphery of the sleeve which is nearer either one of thetwo ends of the sleeve. This bearing ball row has an action of a rollerbearing and also contributes to obtain an effect of automatic tilting,while the opposite side sleeve portions have an action of a slidebearing. Therefore, great load is not applied solely on the bearing ballrow, and wear of components is kept at a lower level. Further, since thecircumferential or annular groove is provided mid way between theopposite ends of the roller, the tilting angle range is symmetrical onthe opposite sides.

Further, since the roller consists of the elastic rubber cylinder andthe sleeve formed directly on the inner side thereof, it is simplifiedin construction and reduced in weight in comparison to the prior artroller, so that the roller is reduced in inertia. Therefore, there canbe provided a small roller suitable for using as a tape guide roller ofthe tape recorder noted above, which is required to frequently repeatoperations of start, stop and reversal and also to be used continuouslyfor long time. Further, as the roller can be reduced in size, it is bestsuited as a small roller of the said type.

Further, since the inner side of the roller is constituted by the sleevehaving low friction coefficient and low wear coefficient, the rollerwill rotate smoothly and will not be worn partially.

Still further, the gap between the inner periphery of the sleeve and theouter periphery of the shaft can be set freely to get a requiredinclination angle of automatic tilting, because they are molding parts.Further, the groove in the sleeve can be easily processed to obtain adesired depth prior to assembling according to the diameter of thebearing balls used. Thus, it is possible to ensure very high freedom ofdesign and reduce cost.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects, features and advantages of the invention will be bestunderstood from the following description with reference to theaccompanying drawings, in which:

FIG. 1 is an enlarged-scale elevational view, partly in section, showinga first embodiment of the invention;

FIG. 2 is an elevational view showing a shaft in the embodiment of FIG.1;

FIG. 3 is an enlarged-scale elevational view, partly in section, showinga second embodiment of the invention without a retainer for bearingballs;

FIG. 4 is an enlarged-scale plan view showing a retainer with bearingballs fitted therein;

FIG. 5 is a plan view, partly in section, showing the retainer;

FIG. 6 is a side view showing the retainer of FIG. 5;

FIG. 7 is an enlarged-scale front view, partly in section, showing athird embodiment of the invention;

FIG. 8 is an enlarged-scale front view, partly in section, showing afourth embodiment of the invention;

FIG. 9 is a fragmentary view, partly in section, illustratingexaggeratively the roller of the embodiment of FIG. 8 in a tilted state;and

FIG. 10 is an enlarged-scale front view, showing the prior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, the invention will be described in conjunction with the illustratedembodiments.

The sleeve used in the invention is composed of polytetrafluoroethylene(fluoroplastics) as a main composition and incorporated with specialfillers, and physical properties of the sleeve are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                                            Sample                                                    Physical Property (Unit)                                                                            No. 1    No. 2                                          ______________________________________                                        Density (lbs./ft..sup.3)                                                                              118.6    124.8                                        Hardness (Durometer D)                                                                               63       65                                            Tensile Strength (lbs./in..sup.2)                                                                     995.4    2346.3                                       Tensile Elongation (%)                                                                               100      200                                           Compressive Strength (lbs./in..sup.2)                                         1% deformation          1094.9 1166                                           5% deformation        3598     2744                                           0.2% offset           2503     1820                                           Compressive Elastic Modulus (lbs./in..sup.2)                                                        109494   116604                                         ______________________________________                                    

The sleeve material used for sample No. 1 had the friction coefficientK;

    K=1.4×10.sup.-11 (in..sup.3 ·min.)/(lb.·ft.·hr.)

when the PV value was 28×10³ lbs./in.² ·ft./min., and the opposingmember was an aluminum shaft made of ADC (Aluminum Die Casting)-12, andits hardness was HRC-22 (Hardness in Rockwell C-scale), and its surfaceroughness Rmax was 0.433 mil to 0.512 mil.

On the other hand, the sleeve material used for sample No. 2 hadcoefficient of friction K;

    K=2.8×10.sup.-12 (in..sup.3 ·min.)/(lb.·ft.·hr.)

when the PV value was 84×10³ lbs./in.² ·ft./min., and the opposing shaftmember was the same as that of sample No. 1.

However, it is sufficient that coefficient of friction K is less than1.4×10⁻¹¹ (in.³ ·min.)/(lb.·ft.·hr.), when the PV value is 28×10³lbs./in.² ·ft./min.

As the material for the sleeve meeting the above requirements, there wasused "Excelide 9550-No. 5" or "9550-No. 7" of Nichias Co., Ltd. at thetime of the present invention, but this material is by no meanslimitative, and any material may be used so long as the aboverequirements are met.

The coefficient of friction was calculated on the basis of an equation;

    K=(W)/(P·V·T·ρ·S)

where,

W: Worn-out Weight (lbs.)

P: Load on unit projected area of sample (lbs./in.²)

V: Surface (Peripheral) Velocity (ft./min.)

T: Time (hr.)

ρ: Density of sample (lbs./in.³)

S: Projected area of sample (in.²)

EMBODIMENT 1

FIGS. 1, 2, 4 and 6 illustrate a first embodiment of the invention.Reference numeral 10 designates a roller. A surface layer of the roller10 is constituted by an elastic rubber cylinder 11. An inner layer ofthe roller 10 consists of a sleeve 12, which is mainly composed ofpolytetrafluoroethylene having the said physical properties andincorporated with a special filler material. The two members, namely thecylinder 11 and the sleeve 12, may be formed as respective one-piecemolding and then subsequently made integral. Alternately, one of thesemembers may be first formed by molding, and then the other member may beformed by insert molding method. The sleeve 12 has a uniform innerdiameter over the entire length.

Reference numeral 15 designates a shaft. The shaft 15 has acircumferential or annular groove 16 on a middle portion thereof, whichis positioned at a middle point or mid way between the opposite ends ofthe roller 10 when the shaft 15 is fitted in the roller 10. A pluralityof bearing balls 30 are provided in the groove 16 in a row. The row ofbearing balls 30 is formed such that the bearing balls 30 are in rollingcontact with the inner periphery of the roller 10 and a bottom of thegroove 16. The rolling surface of the bottom 17 of the groove 16 has anU-shaped sectional shape, which has a radius equal to that of thebearing ball 30. The groove 16 has a width b which is greater than thediameter of the bearing ball 30.

The shaft 15 has a pair of tapered surface portions 18 which are formedon the opposite sides of the groove 16 and faced to the opposite ends ofthe roller 10. The diameter of each tapered surface portion 18 becomesgreater toward the groove 16 and becomes smaller toward thecorresponding end of the roller 10. The angle θ between a generationline O₂ of the tapered surface portion 18 and the axis O, of the shaft15 may be about 0.5° to 15°. In case of this embodiment, it is setwithin a range of 0.5° to 5°. Extension surface of each tapered surfaceportion 18 is in contact with a spherical surface of said bearing balls30 or slightly inside of the spherical surface.

The shaft 15 is provided with a pair of non-contact shaft portions 19located between the groove 16 and each tapered surface portion 18. Thenon-contact shaft portion 19 has a considerably smaller outer diameterthan the inner diameter of the roller 10. The ratio between the axiallength l, of tapered surface portion 18 and the axial length l₂ of thenon-contact shaft portion 19 may be about 1:5 to 5:1, and it ispreferably 1:2 to 2:1.

Although the material of the shaft 15 is not limited, but annealed steelor stainless steel are most preferred in view of wear resistance andcost. Aluminum is particularly suitable to reduce the shaft weight andto obtain a required heat radiation property. Brass and other similarmaterial may also be used.

Stainless steel balls, synthetic resin balls and ceramic balls are usedas the bearing balls 30 suitably in dependence on the material andhardness of the shaft 15. Usually, balls having substantially the samehardness as the shaft 15 are used.

A retainer 25 for holding the bearing balls 30 at a predeterminedinterval from one another in the groove 16 of the shaft 15 is of aring-like form, as shown by FIGS. 4 and 5. More particularly to say, theretainer 25 is opened in the direction at right angles to the axisthereof, so that it has opposite engaging ends 26 which are connected toeach other. When no external force is applied to the retainer 25, theradius R of curvature of its inner surface is substantially the same asthe radius of the largest diameter portion of the shaft 15. When theengaging ends 26 are connected to each other, the retainer 25 forms aperfect ring. At this time, the inner diameter D₁ of the retainer isgreater than the diameter of the bottom 17 of the groove 16 of thesupporting shaft 15, and the outer diameter of the retainer 25 issmaller than the inner diameter of the roller 10. Ball supporting holes27 are radially formed in the retainer in a circumferentially spacedrelation to one another, such that the bearing balls 30 can be supportedat a uniform angular interval.

The material of the retainer 25 is not limited so long as it hasslightly elastical deformablity, low coefficient of friction, excellentheat resistance to the friction heat, and low coefficient of thermalexpansion. At the time of the application, polyamidoimid (PAI) resins ofthermoplastic were best suited.

When the bearing balls 30 are inserted in the ball supporting holes 27,they are capable of sliding rotation in the ball supporting holes 27.The engaging ends 26 of the retainer are provided with a tenon 28 and amortise 29 respectively, which can be connected by hooking with eachother.

The upper end of the supporting shaft 15 is provided with a flange 20,and the lower end of the shaft 15 is provided with a flange 21, eachhaving a diameter greater than the inner diameter of the roller 10 sothat the roller 10 will not move vertically. The end surface of each ofthe flanges 20 and 21 facing on the end surface of the roller 10 has asecond tapered surface 22 of an acute angle, which is formed at rightangles to the generation line O₂ of the tapered surface portion 18. Whenthe roller 10 is inclined or tilted, the ends of the roller 10 will notstrike the flanges 20 and 21, but they are supported with the secondtapered surfaces 22.

The flange 20 at one end of the shaft 15 is detachably mounted on theshaft 15 by a small bolt 23 screwed into the axis portion of the shaft15.

In assembling the above components, the retainer 25 is moved axiallyfrom one end of the shaft 15 up to the position of the groove 16 byincreasing its diameter with making use of its elastic deformation.Then, the tenon 28 and the mortise 29 of the respective engaging ends 26of the retainer 25 are hooked on each other in the groove 16, so as toobtain the retainer 25 of a perfect ring-like form. Then, the roller 10is quietly fitted on the shaft 15 from the top end thereof up to aposition, at which the roller 10 strikes the flange 21 integral with theshaft 15.

Then, another flange 20 is fitted on the top end of the shaft 15, andthe small bolt 23 is screwed via a suitable washer 24, thus securing theflange 20 to the shaft 15.

In using the assembled roller as a tape guide roller of a video taperecorder, an angular stem 15a of the shaft 15 is secured to a particularposition of the frame of video tape recorder.

OPERATION AND EFFECTS OF EMBODIMENT 1

When the small roller structure of this embodiment is used, thefollowing operation and effects are obtained in addition to those of theinvention.

Since the bearing balls 30 are held by the retainer at a predeterminedangular interval in the groove 16 of the shaft 15, they will never bebrought into contact with one another on account of their intervalchanges. They will never be displaced in the groove 16 also in the widthdirection of the groove 16. Further, since the retainer 25 is made ofthe material as noted above, even if the bearing balls 30 are in slidingcontact with the bearing balls 30 and the supporting shaft 15, frictionresistance may be kept at a lower level, and hence, there is nopossibility of spoiling mechanical characters, even if heat is generatedon the contact portions on account of friction heat.

Further, since the second tapered surfaces 22 on the upper and lowershaft flanges 20 and 21 are formed such that their generation linesincline at right angles to those of the tapered surface portions 18, theends of the sleeve 11 of the roller 10 are supported by the secondtapered surfaces 22 with sliding on the generation lines of the secondtapered surfaces 22. Therefore, even if the roller 10 is tilted inrelation to the supporting shaft 15, it does not cause to increase thefrictional resistance substantially.

Further, since the sleeve 12 made of the above material is fitted intothe rubber cylinder 11 in order to constitute the inner periphery of theroller 10, the frictional coefficient is very low. Therefore, even if atape running speed which is several times (i.e., 3 to 5 times) that ofthe ordinary video tape recorder known at the time of the applicationmay be adopted, a sufficiently normal operation can be ensured for thepermissible life period of the video tape recorder.

Further, when annealed steel is used as the material for the shaft 15,the shaft 15 will not be worn at all. When aluminum is used for theshaft 15, satisfactory heat conduction can be obtained. Therefore, noheat is retained or accumulated on the bearing balls 30 and the tapersurface portions 18, and there is no possibility of thermal seizure atall.

The illustrated structure is enlarged in scale. In the case of thisembodiment, the actual length of the roller 10 is about 0.196 to 0.787inch, and the roller 10 has an inner diameter of 0.118 to 0.196 inch andan outer diameter of 0.196 to 0.393 inch, and the bearing ball 30 has adiameter of 39.3 mil to 59 mil, and the shaft has an outer diameter of0.114 to 0.188 inch at the said non-contact shaft portion 19.

The small roller structure of the sizes noted above was actually rotatedat a rotation speed of 2,000 r.p.m. or more, but there was never occuredany phenomenon such that would cause thermal seizure or defectiverotation.

EMBODIMENT 2

FIG. 3 shows a second embodiment of the invention. In this embodiment,the retainer 25 used in the first embodiment is omitted. Partsdesignated by the same reference numerals as those in the firstembodiment are those having like operation and effects.

In this case, when the same sizes as in the first embodiment wereselected, no actual troubles occurred in use at a rotation speed of2,000 r.p.m. or below.

In each case of the embodiment 1 and the embodiment 2, since an actualcontact surface velocity between a shaft and an inner periphery of aguide or pinch roller of usual video tape recorders is relatively lowsuch as 1.125 ins./sec. to 2 ins./sec., and an actual contact surfacepressure therebetween is 1.98 lbs. to 3.09 lbs., the rotation speed ofthe roller is 140 r.p.m. to 204 r.p.m. when the inner diameter of theroller, for example, is 2/16 inches. This value is very low incomparison to the above permissible rotation speed, and hence it is wellunderstood that the small roller structure of the invention has anadequate utility and usefulness.

EMBODIMENT 3

FIG. 7 shows a third embodiment. In this embodiment, the taper surfaceportions 18 of the shaft 15 are omitted so that the shaft 15 has auniform diameter except for the groove 16. The gap D between the outerperiphery of the shaft 15 and the inner periphery of the roller 10 isset about 4 mil to 8 mil, so that the roller 10 is tiltable by about 1°to either side with respect to the shaft 15.

In order that the roller 10 will not be detached from the shaft 15, awasher 37 is in contact with the end surface of the roller 10, and thewasher 37 is held by a spring washer 36 which is fitted on theengagement groove 35 provided at the end of the shaft 15.

In FIG. 7, parts designated by the same reference numerals as those inthe first embodiment are those having the same operation and effects ofthe first embodiment.

A peculiar operation of this embodiment is that the roller 10 istiltable with respect to the shaft 15 in a range of about 1° until theend of the inner periphery of the roller 10 is brought into contact withthe supporting shaft 15.

In this embodiment, since the shaft 15 and inner periphery of the roller10 are brought into contact with each other only at the opposite ends,the contact surface area is reduced so as to decrease loss by friction.

While the operation is continued for long time, the sleeve 12constituting the inner periphery of the roller 10 is worn out. After atapered surface 12a of which diameter increases toward the opposite endsof the roller has been formed as shown in FIG. 9, the contact surfacearea is also increased, so that subsequent wear is extremely reduced. Inthis way, when the sleeve 12 is worn out, the tilting angle of theroller 10 with respect to the shaft 15 is increased, but it does notgive any inconvenience to the operation of the roller.

EMBODIMENT 4

FIG. 8 shows a fourth embodiment. A peculiar construction of thisembodiment is that the inner periphery of the sleeve 12 is formed with acircumferential or annular groove 16 for receiving the bearing balls 30.The sleeve 12 has a uniform inner diameter over the entire length exceptfor the groove 16, and the shaft 15 has a uniform outer diameter overthe entire length. The gap D is substantially of the same size as in thethird embodiment. Parts designated by the same reference numerals asthose in the other embodiments are those having the same operation andeffects.

In this embodiment, since the shaft 15 is free from any groove 16, theshaft 15 may be stronger. Therefore, in providing the same mechanicalstrength of the shaft 15 as in the other embodiments, the diameter ofthe shaft can be reduced. For the rest, the same effects as in the thirdembodiment can be obtained.

What is claimed is:
 1. An automatically tiltable small roller structureof slide bearing support type, comprising:a small roller including anelastic rubber cylinder and a sleeve integral with the inner peripheryof said elastic rubber cylinder, said sleeve composed mainly oftetrafluoroethylene; a shaft fitted in said small roller, said shaft orsaid small roller having a circumferential or annular groove; aplurality of bearing balls fitted in said groove, said bearing ballsbeing provided such that they are in rolling contact with the innerperiphery of said small roller and the outer periphery of said shaft insaid groove, said groove being provided at a middle point between theopposite ends of said roller, said groove having a depth such that saidbearing balls project slightly from said groove, so that a small gap isformed between the inner periphery of said small roller and the outerperiphery of said shaft; and a flange or washer is provided on oppositeends of said shaft and having a diameter greater than the inner diameterof the small roller, so that an inner periphery portion of the roller onone side of said bearing balls and another inner periphery portion ofthe roller on the other side of said balls come into sliding contactwith the outer periphery of said shaft alternately, and end surfaces ofthe roller also come into sliding contact with end surface of saidflange or washer, whereby the axes of said roller and shaft are madeslightly tiltable relative to each other by an angle of 0.5° to 15°. 2.The automatically tiltable small roller structure according to claim 1,wherein said groove is formed on the outer periphery of said shaft, saidshaft has tapered surface portions located on the opposite sides of saidgroove and adjacent to the opposite ends of said roller, said taperedsurface portions each being tapered toward the end of the shaft, theextension surfaces of said tapered surface portions being in contactwith or slightly inside of the outer spherical surface of said bearingballs, portions of said shaft between said tapered surface portions andsaid groove being non-contact portions having a diameter incapable ofcontact with the inner periphery of said roller.
 3. The automaticallytiltable small roller structure according to claim 2, wherein the lengthratio between said tapered surface and non-contact portion of said shaftis 1:5 to 5:1.
 4. The automatically tiltable small roller structureaccording to claim 2, wherein an angle between a generation line of thetapered surface portion and the axis of said shaft is 0.5° to 5.0°. 5.The automatically tiltable small roller structure according to claim 1,wherein said sleeve material has a coefficient of friction of 1.4×10⁻¹¹(in.³ ·min.)/(lb.·ft.·hr) or below, at a PV value of 84×10³ lbs./in²·ft./min., when said fluorplastic sleeve composed mainly ofpolytetrafluoroethylene is fitted on an aluminum shaft and its surfaceroughness Rmax is 0.433 to 0.512 mil, and its hardness is HRC-22 orbelow.
 6. The automatically tiltable small roller structure according toclaim 1, wherein said shaft is made of one member of a group consistingof annealed steel, aluminum, stainless steel and brass.
 7. Theautomatically tiltable small roller structure according to claim 1,wherein said sleeve material has a coefficient of friction between1.4×10⁻¹¹ and 2.8×10⁻¹² (in.³ ·min/lb. ft. hr.) at a PV value of 18×10³to 84×10³ (lb/in.³ ·ft/min.), said fluorocarbon sleeve being composedmainly of tetrafluoroethylene fitted on an aluminum shaft having surfaceroughness of 0.433 to 0.512 mil and hardness not exceeding HRC-22.
 8. Anautomatically tiltable small roller structure of slide bearing supporttype, the structure comprising:a small roller including an elasticrubber cylinder and a sleeve integral with the inner periphery of saidelastic rubber cylinder, said sleeve composed mainly ofpolytetrafluoroethylene; a shaft fitted in said small roller, said shaftbeing provided with an annular groove located at a middle point betweenthe opposite ends of said roller, said shaft being provided with a pairof first tapered surface portions on the opposite sides of said grooveand adjacent the opposite ends of the roller, with the diameter of thefirst tapered surface portion becoming greater toward the groove; aplurality of bearing balls fitted in said groove, said bearing ballsbeing provided such that they are in rolling contact with the innerperiphery of said small roller and the outer periphery of said shaft insaid groove, said groove having a depth such that said bearing ballsproject slightly from said groove, so that a small gap is formed betweenthe inner periphery of said roller and the outer periphery of saidshaft, said gap allowing said roller to tilt relatively in the shaft atan angle in a range of 0.5° to 5°; and a pair of flanges provided atopposite ends of said shaft and having a diameter greater than the innerdiameter of the small roller, said flange being provided with a secondtapered surface portion on its end surface, said second tapered surfaceportion being formed at right angles to a generation line of the firsttapered surface portion, whereby an inner periphery portion of theroller on one side of said bearing balls and another inner peripheryportion of the roller on the other side of said balls can come intosliding contact with each of said first tapered surface portions of theshaft alternately, and end surfaces of said roller also come intosliding contact with said second tapered surface portion of the flange.9. An automatically tiltable small roller structure of slide bearingtype, the structure comprising:a small roller including an elasticrubber cylinder and a sleeve integral with the inner periphery of saidelastic rubber cylinder, said sleeve being composed mainly ofpolytetrafluoroethylene and having an annular groove provided at amiddle point between the opposite ends of said roller; a shaft fitted insaid small roller, said shaft having a flange surface provided at eachend of the shaft; and a plurality of bearing balls fitted in saidgroove, said bearing balls being provided such that they are in rollingcontact with the inner periphery of said groove in said sleeve and withan outer periphery of said shaft, said groove having a depth such thatthe bearings project inwardly slightly from the groove, so that a slightgap is formed between the inner periphery of said small roller and theouter periphery of said shaft, so that an inner periphery portion of theroller on one side of said bearing balls and another inner peripheryportion of said roller on the other side of said balls can come intosliding contact with the outer periphery of the shaft alternately,whereby the axes of the roller and the shaft are made slightly tiltablerelative to each other by an angle of about 0.5°-5°.
 10. Anautomatically tiltable small roller structure of slide bearing typeaccording to claim 9, wherein said gap is 4-8 mil and the tiltable angleis about 1° on either side of the shaft axis.